Bag making machine and method

ABSTRACT

A machine for processing plastic web stock in a continuous manner for making bags. The bags have one or more gusseted portions with diagonal seals at corners thereof. The machine for applying the diagonal seals on the web stock includes a guide structure which is mounted for free floating movement in a direction transverse to the direction of travel of the stock through the machine. The guide structure engages the inner fold of each gusseted portion so as to shift laterally in response to lateral weaving of the stock as it travels through the machine. The mechanism for applying the diagonal seals is mounted to shift laterally as a unit with the guide structure so that the seals will be precisely located relative to the inner fold lines of the gusseted portions.

Uni I tates LaFleur 1451 Dec. 10, 1974 [73] Assignee: Square Bag-ItCorp, Manistee,

Mich.

[22] Filed: Aug. 1, 1973 [21] Appl. No.: 384,611

52 us. (:1 156/306, 83/368, 83/428, 93/DIG. 1, 93/35 813, 156/252,156/515.

51 1m. (:1. 1309 5/00, 133213 31/00, 33% 15/34 [58] Field 01 Search156/242-244,

156/251, 252, 255, 306, 384, 494-496, 500, 504, 515,530, 583; 93/D1G. 1,l4,17-20, 33 H, 35 R, 35 SB; 229/53, 5760; 83/368, 428

Wech 156/515 3,776,804 12/1973 Monahan et all 156/515 PrimaryExaminer-Clift0n B. Cosby Assistant ExaminerJohn E. Kittle Attorney,Agent, or FirmBarnes, Kisselle, Raisch & Choate [5 7] ABSTRACT A machinefor processing plastic web stock in a continuous manner for making bags.The bags have one or more gusseted portions with diagonal seals atcorners thereof. The machine for applying the diagonal seals on the webstock includes a guide structure which is mounted for free floatingmovement in a direction transverse to the direction of travel of thestock through the machine. The guide structure engages the inner fold ofeach gusseted portion so as to shift laterally in response to lateralweaving of the stock as it travels through the machine. The mechanismfor applying the diagonal seals is mounted to shift laterally as a unitwith the guide structure so that the seals will be precisely locatedrelative to the inner fold lines of the gusseted portions.

26 Claims, 19 Drawing Figures 3@3 ,66&

PATENTB, DEC? 019M llllltiillllllllnllllv BAG MAKING MACHINE AND METHODThis invention relates to a bag making machine and method and moregenerally to a machine for performeration of the machine that theinvention is admirably suited for performing a variety of operations ona travelling plastic web having a lengthwise extending fold linetherein.

In the manufacture of many plastic articles from tubular or foldedplastic webs it is necessary to perform some operation on the web at apredetermined location in relation to the side edges or a fold line inthe web material as the stock is fed from a source of supply to awind-up roll or to a cutting and stacking device. When such web stock isfed in a more or less continuous manner (with or without intermittentinterruptions in the feed cycle) there is usually a tendency for the webto weave or shift laterally of its direction of travel at least slightlyas it progresses through the machine. Several elaborate and expensiveweb guiding arrangements have been developed heretofore to maintain thealignment of the travelling web within relatively close tolerances sothat any auxiliary processing operations performed on the web (such assealing, slitting, printing, etc.) will be accurately located inrelation to the side edges or a fold line on the web. In such machinesthe apparatus for performing the auxiliary operation on the web, isnormally in a fixed position and the web is shifted laterally asrequired by the web guiding mechanism while it is being fed through themachine in order to properly align the web with the mechanism forperforming the auxiliary operation thereon.

The present invention has for its primary object the provision of amachine of the type described wherein the apparatus for performing theauxiliary operation on the web is mounted on the machine in a mannerpermitting it to float or shift transversely of the path of travel ofthe web and a fold or gusset in the travelling web is utilized to shiftthis apparatus transversely of the path of travel of the web as requiredso that the auxiliary operation will be performed on the web at alocation accurately aligned relative to the fold line or gusset in theweb.

The machine disclosed herein is illustrated for the manufacture ofplastic bags of the type shown, for example, in my prior US. Pat. No.3,143,277 wherein the bag is provided with an inwardly extending gusseton each side thereof and diagonally extending seals are provided in thegusseted portions of the bag. With bags of this general type it isimportant that the diagonally extending seals terminate at their innerends closely adjacent the apex of the V-shaped gusset in order toprevent leakage from the bag and so that when the bag is filled it isproperly reinforced by the gusset seals. Accordingly, in the form ofmachine illustrated herein a sealing mechanism is mounted on the machineframe by means of rollers or the like which permit the sealing mechanismto shift laterally in relation to the path of travel of the gusseted webthrough the machine. The

sealing mechanism includes guide members which extend laterally inwardlyfrom opposite side edges of the web into the gussets and engage the foldline of the gus set so that the entire guide and sealing assembly shiftslaterally in response to lateral shifting of the web and thus producesseals which are accurately located in relation to the gussets along eachside of the web. In addition, in order to insure proper guiding of thesealing mechanism it is important that the webbe maintained in alengthwise tensioned condition at the section thereof engaged by theguides so that any slight lateral shifting of the web will result in acorresponding lateral shifting of the guide and sealing mechanism.

Other objects and advantages of the present inven-. tion will becomeapparent from the following description and accompanying drawings, inwhich:

FIG. 1 is a side elevational view, partly in section, of a machineembodying the present invention;

FIG. 2 is a fragmentary elevational view in the direction of arrow 2 inFIG. 1;

FIG. 3 is a fragmentary sectional view along line 33 in FIG. 2;

FIG. 4 shows a portion of the assembly illustrated in FIG. 2 on anenlarged scale;

FIG. 5 shows the opposite side of the assembly shown in FIG. 4;

FIG. 6 is a fragmentary sectional view taken along line 6-6 in FIG. 5; i

FIG. 7 is a fragmentary cross sectional view of a portion of the sealingand guide mechanism;

FIG. 8 is a fragmentary elevational view of a modified form of sealingand guide mechanism,

FIG. 9 is a top view of the arrangement shown in FIG. 8.

FIG. 10 is a fragmentary view of a further modified FIG. 15 is aperspective view of'a bag formed from the stock shown in FIG. 14;

FIG. I6 is a fragmentary plan view of plastic stock with the sealpattern produced in accordance with the modification shown in FIG. 10andFIG. 17 shows the bag formed thereby;

FIG. 18 is a fragmentary plan view of the plastic web as processed bythe arrangement shown in FIG. 11;

FIG. 19 illustrates a bag formed from the web stock shown in FIG. 18.

Referring first to FIGS. 1 through 7, the machine illustrated includes aframe, generally designated 10, having means for supporting a supplyroll 12 of tubular plastic web, a wind-up roll 14 for the processed weband means intermediate rolls 12 and .l4 foradvancing the tubular stockthrough the machine. The latter means includes two sets ofintermittently driven pull rolls 16 adjacent the wind-up roll I4 andbetween which is arranged a transverse sealing and perforating mechanism18. The tubular stock is wound on roll 12 in a flattened condition as itemerges from an extruder,

the stock being provided with inwardly extending gussets 20 alongopposite edges thereof. The inner edges of the gussets are defined byfold lines 22. As the stock, generally designated 24, is unwound fromroll 12 it is caused to travel around a pair of dancing rolls 26 andidler rolls 28 in a conventional zig-zag fashion and then past asnubbing device 30 which engages the stock to prevent reverse movementthereof as might otherwise be produced by the freely vertically movabledancing rolls 26. As the stock travels past snubber 30 it wraps around acontinuously driven roll 32 against which it is maintained in frictionalengagement by idler rolls 34, 34a. The web then travels verticallyupwardly through a sealing mechanism, generally designated 36, around avertically shiftable web relaxing roll 38 and then around a verticallyadjustable top roll 40. The web is then directed in a downwardlydirection between friction rolls 42, 44, through another sealingmechanism 46 and then upwardly around an idler roll 48. It then travelsover a second vertically adjustable roll 50 to the intermittently drivenpull rolls 16. Wind-up roll 14 is suitably driven to wind up the web asit is fed by pull rolls 16. A conventional drive is utilized for thispurpose. Likewise, a conventional drive is utilized for rotating pullrolls 16 intermittently.

A shaft 52 on which is fixed a cam 54 is driven continuously at apredetermined speed in relation to the speed of rotation of pull rolls1'6. Sealing mechanism 18 includes a vertically reciprocable heating andperforating element 56 which is actuated by a cam follower 58 engagingcam 54 such that, when the rotation of pull rolls 16 is arrested, theheat sealing element 56 is lowered into contact with the web stock toform a transverse seal therein as indicated at 60 in FIGS. 14, 16 and18. Element 56 is also designed to form a transverse perforation line 61(FIG. 14).

Shaft 52 also has a drive pulley oragear 62 mounted thereon which isconnected as by a chain or belt 64 with a driven gear or pulley 66 on asecond shaft 68 journalled on frame 10. Two cams 70, .72 are keyed toshaft 68. Cam 70 is engaged by a cam follower 71 to verticallyreciprocate a link 74 connected to a lever 76 which supports roller 38at one end. The opposite end of lever 76 has a fixed pivotal connectionas at 78 on frame 10. When lever 76 is raised to the solid line positionshown in FIG. 1 it cooperates with dancing rolls 26 to maintain the webstock in a tensioned condition between supply roll 12 and the first setof pull rolls 16. When the cam follower 71 at the lower end of link 74engages the recessed portion of cam 72 lever 76 swings downwardly to thebroken line position and relaxes the tension in the web between snubber30 and the pull rolls 16. The rotation of pull rolls 16 is coordinatedwith the rotation of cam 72 such that their rotation is arrested whilecam follower 71 is in engagement with the recessed portion of cam 72.Thus, the stock is fed intermittently through the machine and, when itsforward movement is arrested, the tension in the web is relaxed.

An auxiliary frame 80 is guided for horizontal movement on frame by aplurality of guide rollers 82. Frame 80 is biased in a direction towardthe right as viewed in FIG. 1 by a compression spring 84. A cam follower86 on frame 80 engages the periphery of cam 70 to normally maintainspring 84 compressed, but at regularly spaced intervals, to permit frame80 to shift in a direction toward the right. It will be observed thatthe recessed portion 88 of cam is related in a circumferential directionto the recessed portion 90 of cam 72 such that frame 80 shifts to theright when roller 38 is in the lowered position and the tension on theweb is relieved.

The two sealing mechanisms 36, 46 are adapted to form diagonal seals onthe gusseted portions of the tubular stock, such as indicated at 92 inFIG. 14. Both of these sealing mechanisms are of generally the sameconstruction. Each of these sealing mechanisms comprises a pair ofseparate rigid upright struts 94, each having an angularly inclinedbracket 96 at its upper end on which is journalled a roller 98. Eachroller 98 is supported on a shoulder of a horizontally extending anglemember on'frame 10. The angle member associated with sealing mechanism36 is designated as 100a and the angle member associated with sealingmechanism 46 is designated as 10%. A second roller 102 is journalled atthe lower end of each strut 94 for rotation about a vertical axis. Eachroller 102 is adapted to engage one leg of a horizontally extendingguide channel on frame 10. The guide channel associated with sealingmechanism 36 is designated as 104a and the guide channel associated withsealing mechanism 46 is designated as 104b.

Each strut 94 is also provided with a shallow yoke 106 which is securelyattached thereto and which is shaped to'receive a tie bar 108. A lockingthumb screw 110 is threaded into each yoke 106 for rigidlyinterconnecting the two struts 94 in a fixed, laterally spaced relationby means of tie bar 108. Thus, the two struts 94 can be spaced furtherapart or closer together, as desired, by means of tie bar 108. Eachstrut 94 has a horizontally extending support arm 112 extendinglaterally outwardly therefrom. To the outer end of each arm 1 12 thereis rigidly mounted a tubular brace 114. There is associated with eachstrut 94 a guide plate 116, the laterally outer edge of which isreinforced by an angle 118. Each guide plate 116 is rigidly connected totubular brace 114 so as to extend vertically in spaced relation to strut94 (see FIG. 6).

The adjustable tie bar construction described enables the two guideplates 116 on each sealing mechanism to be spaced apart so that theirvertically extending, inwardly opposed edges 120 (FIG. 5) can be spacedhorizontally apart to correspond with the horizontal dimension betweenthe two fold lines 22 of gussets 20 on the tubular stock 24. This isillustrated in FIG. 3. With the guide plates 116 so adjusted andextending into the gussets 20 it will be appreciated that the mechanismsupported on each set of rollers 98, 102 is free to shift laterally asthe web stock 24 weaves sidewise relative to its path of travel.

More specificially, with reference to scaling mechanism 36 it will beobserved that, since the web stock wraps around roller 34 and aroundroller 38, when it is in a tensioned condition the frictional engagementof the travelling web with rollers 34 and 38 will maintain the portionof the web between these rollers in a relatively taut condition. Byreason of the manner in which the tubular stock is manufactured and thegussets 20 formed therein, the distance d between the fold lines 22 isvery uniform. When the guide plates 116 are adjusted so that their inneredges are spaced apart corresponding to the distance d and since the webis relatively taut between rollers 34 and 38 when roller 38 is in theraised position, it follows that as the web shifts laterally the rollersupported guide plates 116 likewise shift lattendency for the web toflex laterally in response to the lateral force applied thereto by guideplates 116 is minimized by the fact that the web is in a tensionedcondition and frictionally engaged adjacent the upstream and downstreamends of sealing mechanisms 36, 46. This is an important feature of thepresent invention since the sealing mechanisms are supported by thestructure which supports guide plates 116. Thus, each vertical strut 94and the components supported thereby can be considered as a carriagewhich is free to shift laterally on frame to correspond with the lateralshift ing or weaving of web 24 between rollers 34 and 38. With respectto sealing mechanism 46 on the opposite side of frame 10, the functionof rollers 34 and 38 insofar as frictional engagement with the web isconcerned is performed by rollers 48 and 44, respectively.

Referring now to FIGS. 5 through 7, it will be observed that on one sideof guide plate 116 and spaced parallel thereto there is rigidly attachedto tubular brace 114 a tubular arm 122. Each arm 122 has a pair oftubular brackets 124 rigidly mounted thereon in vertically staggeredrelation (FIG. 5). A heat sealing bar 126 having an electricallyenergized heater 128 mounted thereon extends generally diagonally ofeach guide plate 116. Each heat sealing bar 126 has a tubular member 130fixedly attached thereto. A pair of horizontally extending pins 132 arefixedly mounted on tubular member 130 and extend horizontally throughtubular brackets 124 to enable heat sealing bar 126 to be shiftedhorizontally toward and away from its respective guide plate 116.Springs 134 normally bias heat sealing bars 126 to a retracted positionspaced from its respective guide plate 116. Horizontally movable frame80 has a pair of flattened tubes 136 fixedly attached thereto andhorizontally positioned to register with the guide pins 132 of sealingmechanisms 36 and 46. Thus, when the cam follower 86 encounters therecessed portion 88 of cam 70, frame 80 shifts to the right under theinfluence of compression spring 84 so that the tubes 136 engage guidepins 132 and shift both heat sealing bars 126 toward the respectiveguide plates 116.

Referring now to FIGS. 4 and 6, it will be observed that on the side ofeach guide plate 116 opposite the heat sealing bar 126 there is aback-up bar 138. Each back-up bar 138 is rigidly connected to strut 94by a rigid strap 140. Each back-up bar 138 registers with its respectivediagonally inclined heat sealing bar 126.

Referring now to FIG. 5, it will be observed that each guide plate 116has a diagonally extending slot 142 therein which registers with theheat sealing edge portion 144 of each heat sealing bar 126. Edge portion144 of each heat sealing bar extends over each slot 142 to the inneredge 120 of each guide plate 116. Each slot 142 extends diagonallydownwardly from the inner edge 120 of each guide plate 116 to adjacentthe outer edge of the guide plate as shown in FIG. 5. A Teflon web 146loosely spans slot 142 throughout the length thereof and is attached tothe face of guide plate 116 which is adjacent the heat sealing bar 126as shown in FIG. 7. Edge portion 144 of heat sealing bar 126 also has astrip of Teflon 148 attached thereto. FIG. 7 also illustrates the factthat back-up bar 138 is likewise axially'aligned with slot 142 oppositeheat sealing bar 126. Onthe face thereof adjacent guide plate 116back-up bar 138 is provided with a cushion 150 and the entire assemblyis wrapped with a Teflon covering 152.

As mentioned previously, sealing mechanism 46 is generally the same assealing mechanism 36. However, it will be appreciated that, when the webstock 24 is threaded through the machine and guide plates 116 in themanner shown in FIG. 3, heat sealing bar 126 of heat sealing mechanism36 is designed to act upon the two overlying plies of the web at oneface thereof and the heat sealing bar 126 of heat sealing mechanism 46is adapted to act upon the two overlying plies of the web at the otherside thereof. Referring to FIG. 7, the heat supplied to heat sealing bar126 through heater 128 is controlled such that, when the heat sealingbar 126 is shifted to the right to apply pressure to all four plies ofthe web between the heat sealing edge portion 144 and cushion 150, theheat is only sufficient to form a weld joint between the two plies ofthe web at the left of the guide plate 116. The Teflon members 146, 148and 152 prevent the heated plastic web from sticking to the opposedmembers by means of which heat sealing pressure is applied to the web.Since the heat sealing bars 126 are caused to contact the web when theweb is in a relaxed position, the two heat sealing mechanisms 36, 46produce the weld seams 92 shown in FIG. 14 on each of the four sets oftwo plies at opposite edge portions of the web. The tension in the webis relaxed and the feed is arrested for a period of time to allow theweld seam to solidify and withstand the tension subsequently appliedthereto when roll 38 is again raised and rotation of pull rolls 16 isresumed. Furthermore, it will be observed that the slots 142 in eachguide plate 116 enables the plies of the web to be sealed from the outerside edge portions thereof directly to the fold lines 22. This resultsnot only in a bag 154 (FIG. 15) having a reinforced bottom corners, butalso in a bag the square bottom of which is absolutely leakproof andadapted to contain lliquids or other free flowing materials. If theseals 92 did not extend directly to the fold lines 22, but insteadterminated short thereof, a small opening would be formed in the bottomof the bag at the joints between the fold lines 22 and the seals 92. Ifseals 92 extended beyond fold lines 22, when the individual bags aresevered from the stock the upper ends thereof would have unwantedlocalized seams therein.

It will be appreciated that roller 40 is vertically adjustable so thatthe heat sealed seams 92 at one side of the bag will register accuratelywith the heat sealed seams 92 at the opposite side of the bag. Likewiseit will be appreciated that roll 50 is vertically adjustable so that thetransversely extending seam 60 and/or the perforation line 61 producedby the mechanism 18 will register accurately with the inner ends ofseams 92.

In the modification illustrated in FIGS. 8 and 9 the two heat sealingassemblies are mounted in directly opposed relation on opposite sides ofthe same guide plates. Thus, in this modification the two guide plates156, 158 are mounted on two carriages 160, 162. The two carriages 160,162 are adjustably interconnected in spaced relation by means of tiebars 164, 166. The carriages are provided with rollers 168, which enablethe two carriages to shift as a unit freely on horizontally extendingrails 172, 174 on the frame of the machine. The two guide plates 156,158 are constructed similarly to guide plates 116 shown in FIG. 7 withthe Teflon I web 146 extending across the diagonal slot in the guideplate. However, the heat sealing bars 176, 178 are arranged on oppositesides of guide plates 156, 158 in alignment with the slots therein. Inthe arrangement illustrated in FIGS. 8 and 9 the two sets of heatsealing bars 176, 178 are simultaneously actuated by air cylinders orsolenoids 180 to form all four diagonal seals 92 in the plastic web atthe same time. In this arrangement the Teflon web corresponding to thatshown at 146 in FIG. 7 prevents the two plies adjacent one face of theweb from sticking to the two plies at the opposite face of the web. Inmost other respects the arrangement shown in FIGS. 8 and 9 issubstantially the same as that shown in FIGS. 1 through 7. However,since heat sealing bars 176, 178 are in opposed relation, a back-up bar(such as shown at 138 in FIG. 7) is not required. Likewise, in themodification shown in FIGS. 8 and 9 the machine does not require ahorizontally movable frame such as shown at 80 in FIG. 1; instead a camcorresponding in function to cam 70 may be utilized for triggeringelements 180.

The arrangement shown in FIG. 10 is used in conjunction with plastic webstock 182 having a single gusset 184 at only one edge thereof. The guideplate 186, which extends inwardly of gusset 184 with its inner edgeengaging the fold line 188, is guided for horizontal movement betweenrollers 190 on a stationary portion 192 of the machine frame. Guideplate 186 is urged in a direction inwardly of gusset 184 with a verylight pressure by a very light counterweight 194. Obviously a very lightspring could be used in place of counterweight 194. The two heat sealingbars 196 are mounted by structure (not shown) to move horizontally withguide plate 186 and are caused to advance toward each otherintermittently to form the two diagonally extending seals 198, 200 onthe gusseted portion 184 of the web 182 (FIG. 16). When the web 182 issevered through the transversely extending seals 60 a bag 202 isprovided wherein the gusseted portion 184 forms the bottom 204 of thebag. In this embodiment seals 60 are of sufficient width so that a lineof perforations can be applied therethrough without disturbing the sealon each side thereof and thus provide successive bags with the seals 60extending along the end edges thereof.

A further modification of the present invention is shown in FIGS. 11through 13. In this arrangement the plastic web stock, generallydesignated 206, is of flattened tubular cross section with inwardlyextending gussets 208 along opposite edges thereof similar to that shownin FIG. 3. In this arrangement two guide plates 210 are interconnectedin adjustably spaced relation by a tie bar 212. Guide plates 210 arespaced apart such that their inner edges 214 engage the fold lines 216of the two gussets 208. The two guide plates 210 interconnected bythetie bar 212 act as a carriage which is movable freely in a horizontaldirection on the frame of the machine by means of guiding rollers 218.Intermediate the upper and lower edges thereof each guide plate 210 isformed along its inner edge with a rectangularly-shaped recess 220. AV-shaped heating element 222 is mounted on each guide plate 210 and ispreferably bent as shown in FIG. 12 so that it extends into recess 220in the plane of its respective guide plate 210. The apex 224 of eachheater 222 is axially aligned with the guiding edge 214 of itsrespective guide plate 210. A Teflon web 226 is wrapped around the inneredges of guide plates 210 so as to overlie the opposite faces of heater222. At the side of each guide plate 210 opposite tie bar 212 there isarranged on the machine a pair of movable platens 228 which overlie theV-shapecl heaters 222. The operating faces of platens 228 and tie bar212 adjacent the gusset 208 are coated with Teflon or other suitablematerial which prevents the heated plastic web from sticking thereonwhen the platens are actuated to apply pressure to the gusseted portionsof the web stock 206 while heaters 222 are energized. Heaters 222 arepreferably of the impulse type which cool immediately after a shortheating cycle. This results in a rapid cooling of the heat seals so thatthey can withstand the required tension when the stock is fed againimmediately following a heat sealing operation. Rapid cooling of theseals is required for high production rates when all four seals areformed simultaneously.

The modification shown in FIGS. 11 through 13 produces a finished web ofthe type shown in FIG. 18. In this arrangement two V-shaped seals 230are simultaneously formed at the gusseted portions 208 at each side ofthe plastic web 206. A slitting knife (not shown) is mounted on thehorizontally movable carriage structure (guide plates 210 or tie bar212) so as to slit the web lengthwise centrally between the inner foldlines of the gusseted portions as indicated at 232 in FIG. 18. Thus, thearrangement shown in FIGS. 11 through 13 is adapted to form two sets ofbags simultaneously, one of which is shown at 234 in FIG. 19. From thestandpoint of its construction bag 234 is similar to bag 202 illustratedin FIG. 17.

In each of the embodiments illustrated it will be observed that a freelyfloating guide structure is provided which engages within a fold orgusset in the web stock being fed so as to shift horizontally inaccordance with the lateral weaving or shifting of the web. While theweb is being fed, it is maintained in a tensioned condition and theportion of the web being acted upon by the guide structure is preventedfrom flexing laterally in response to the lateral forces applied theretoby the guide structure. This results from the fact that on the upstreamand downstream sides of the guide structure the tensioned web isfrictionally engaged (such as by rollers 34, 38 and 44, 48). Thisfrictional engagement prevents .the web from shifting sidewise on therolls while in a tensioned condition.

In each instance the apparatus for performing an operation on the web(the heat sealing mechanisms in the embodiments illustrated) is mountedto shift laterally with the guide structure so that the operationperformed on the web is always in a predetermined position in relationto the fold line engaged by the guide structure. Thus, if the web weavesslightly from side to side as it travels through the machine (and thisinvariably occurs), the operation performed on the web is alwaysprecisely located with reference to the fold lines on the web engaged bythe guide structure. While the embodiments illustrated show the formingof heat sealed seams on the web, it will be appreciated that theappartus operating on the web could also be or include a printingdevice, a punching or slitting device, or any other type of apparatuswhich might be utilized for performing an auxiliary operation on thetravelling web. In order to prevent the web from tearing at the heatedseals, the tension on the web is relaxed while the heat sealingoperation is being performed.

I claim:

1. In a machine for performing an auxiliary operation, such as sealing,slitting, printing or the like, on a continuous length of a flexibleplastic web having a longitudinally extending fold therein thecombination comprising, a frame, means on said frame for feeding saidweb in a lengthwise direction, means on said frame at one zone in thepath of travel of the web for maintaining the web in a lengthwisetensioned condition so that the line of folding follows a generallystraight path, carriage means on said frame at said zone mounted forrelatively free movement in a direction transversely to the path oftravel of the web and in a plane generally parallel to the plane of theweb, guide means on said carriage means adapted to extend into andbetween the folded plies of the web and engage the web at the fold linefor causing the carriage to shift laterally on said frame in response tolateral weaving of the fold line of the web as the web travels throughsaid zone, and means carried by and movable with said carriage means forperforming said operation on the portion of the web travelling throughsaid zone, said operation performing means being disposed adjacent saidguide means so that the operation performing means acts on said webadjacent the portion thereof engaged by the guide means.

2. The combination called for in claim 1 including means at the inletand outlet ends of said zone frictionally engaging said web andresisting lateral flexing thereof in response to lateral forces appliedto the web by said guide means as the tensioned web travels through saidzone.

3. The combination called for in claim 1 including a roller at the inletend of said zone around which the web is caused to travel in a tensionedcondition, and means for directing the web to said roller such that theweb approaches the roller in a plane inclined to the plane of the web asit travels through said zone, said tensioning means causing the web tofrictionally engage said roller to minimize the tendency of the web toflex laterally in response to lateral forces applied to the web by saidguide means. 1

4. The combination called for in claim 1 including a roller adjacenteach of the opposite ends of said zone, said rollers extendingtransversely of the path of travel of the web, said two rollersdirecting said web in a rectilinear path therebetween so that the webassumes a flat plane at the portion thereof extending between therollers, said web being directed to one of said rollers and away fromthe other roller at angles inclined to said flat plane so that thetensioning means causes the web to frictionally engage the periphery ofsaid rollers and thus minimize the tendency for the web to flexlaterally in response to lateral forces applied thereto by the guidemeans as the web travels through said zone.

5. The combination called for in claim 41 wherein said guide means aredisposed intermediate said two rollers in the path of travel of the web.

6. The combination called for in claim I wherein said operationperforming means comprises a heat sealing member for applying a weldedseam to the plastic web in a predetermined position relative to the foldline therein.

7. The combination called for in claim 1 wherein said web is formed witha V-shaped gusset extending inwardly from a side edge thereof and saidguide means extend laterally inwardly of said side edge and engage thefold line defining the apex of the V-shaped gusset.

8. The combination called for in claim 7 wherein the gusseted portion ofthe web defines four plies of said web adjacent said one edge and saidoperation performing means acts upon two of the plies at one side of theguide means.

9. The combination called for in claim 7 wherein the gusseted portion ofthe web defines four plies of said web adjacent said side edge, saidguide means engaging the fold line of said gusset at two longitudinallyspaced portions thereof, said operation performing means being disposedbetween said longitudinally spaced portions and between the two innerplies of said web.

10. The combination called for in claim 9 wherein said operationperforming means comprises heat sealing means adapted to form a weldedseam on the gusseted portion of the web extending inwardly to said foldline in a direction inclined at an acute angle to the path of travel ofthe web.

11. The combination called for in claim 1 wherein said web comprises aflattened tubular member having a V-shaped gusset extending laterallyinwardly from each side thereof, said guide means comprising a pair oflaterally spaced co-planar members extending laterally inwardly fromeach side edge of the web with the opposite inner edges engaging theopposed vertices of said V-shaped gussets.

12. The combination called for in claim 11 wherein said carriage meanscomprises two carriages, one for each guide means, and means formaintaining said guide means in adjustably fixed laterally spaced rela-'tion so that the inner opposed edges thereof can be spaced apart infixed relation to correspond with the lateral spacing between thevertices of webs having differently sized gussets.

13. The combination called for in claim 12 wherein said last-mentionedmeans comprises a tie bar interconnecting the two guide means, theinterconnection between the tie bar and at least one of said guide meansbeing laterally adjustable.

14. The combination called for in claim 12 wherein said operationperforming means comprises a heat sealing member and a back-up memberdisposed on opposite sides of said guide means in spaced relation to theopposed outer plies of said web and means for relatively moving the heatsealing member and the back-up member toward each other to form a weldedseam on the gusseted portion of the web.

15. The combination called for in claim 1 wherein the guide meanscomprises a guide plate extending laterally inwardly between the pliesof the web and having an inner guiding edge engaging said fold line,said guiding edge having a recess therein, said operation performingmeans comprising a heat sealing member, said heat sealing memberregistering with said recess in the guide plate and extending laterallyinwardly to said fold line so that, when the heat sealing member isactuated, it is adapted to form a heat seal extending inwardly from theside edge of the web directly to the fold line.

16. The combination called for in claim 15 wherein said recess islocated in said guide edge intermediate the ends thereof.

17. The combination called for in. claim 16 including a sheet ofmaterial overlying said recess, said material lll being of the type towhich said plastic web stock will not readily adhere when in a heatedcondition.

18. The combination called for in claim 1 wherein the machine includes asecond zone having a similar. carriage means, guide means and operationperforming means at said second zone, said web stock being of flattubular cross section and having a laterally inwardly extending V-shapedgusset at each side thereof, said guide means at each of said zonesengaging the fold lines comprising the vertices of said two gussets,said operation performing means being disposed adjacent one face of theweb stock at one of said zones and adjacent the opposite face of the webstock at the other zone.

19. The combination called for in claim 18 wherein said operationperforming means comprises a heat sealing member at each of said zoneswhich when actuated is adapted to form diagonal seals through two pliesof the stock at said gussets which extend from the outer side edges ofthe stock inwardly to the vertices of the gussets.

20. The combination called for in claim 19 wherein said two zones arespaced apart in the direction of travel of the stock so that thediagonal seals formed be-' tween two plies of the stock at one zoneregister with the diagonal seals formed between the other two plies ofthe stock at the other zone.

21. The combination called for in claim 17 wherein said heat sealingmember is mounted on said guide plate at said recess and said materialoverlies opposite faces of the heat sealing member.

22. The method of aligning a moving web of plastic material having afold line extending lengthwise thereof in the direction of travel of theweb with an apparatus for performing an operation on the web, such assealing, slitting, printing and the like, comprising the steps of movingthe web lengthwise on a support structure in a tensioned condition andin a rectilinear path between two longitudinally spaced points on saidsupport structure, frictionally engaging the web at said two points tominimize the tendency for the web to flex laterally of its direction oftravel in response to lateral forces applied to the web between said twopoints, engaging the fold line of the web with a guide means positionedbetween said two points, permitting the guide means to shift freely in alateral direction on said support structure in accordance with lateralmovement of the travel of the web between said two points, andsupporting said apparatus for free lateral movement with said guidemeans so that said apparatus is always located laterally in apredetermined position relative to said fold line.

23. The method according to claim 22 wherein said two points are locatedon said support structure closely adjacent said guide means on theupstream and downstream sides thereof.

24. The method according to claim 22 wherein said web is of flat tubularcross section with an inwardly extending V-shaped gusset at each sidethereof and said guide means comprises a pair of laterallyinterconnected guide members extending into said gussets from oppositesideedges of the web and engaging the fold lines defined by the apicesof the two gussets.

25. The method according to claim 22 wherein said web comprises a heatsealable plastic film and said apparatus for performing an operationthereon comprisesa heat sealing means and including the steps ofintermittently arresting thelengthwise movement of said web, relaxingthe tension in the web when its lengthwise movement is arrested andcausing the heat sealing means to engage the web while the web is insaid relaxed condition.

26. The method according to claim 25 wherein the web is flattenedtubular cross section with an inwardly extending V-shaped gusset at eachside edge thereof, said guide means comprising a pair of laterallyinterconnected guide members extending into said gussets from oppositeside edges of the web and engaging the fold lines defined by the apicesof the V-shaped gussets and wherein said heat sealing means are causedto engage the gusset portions of the web to form diagonal seals thereinextending inwardly from the opposite side edges of the web andterminating at said fold lines.

1. In a machine for performing an auxiliary operation, such as sealing, slitting, printing or the like, on a continuous length of a flexible plastic web having a longitudinally extending fold therein the combination comprising, a frame, means on said frame for feeding said web in a lengthwise direction, means on said frame at one zone in the path of travel of the web for maintaining the web in a lengthwise tensioned condition so that the line of folding follows a generally straight path, carriage means on said frame at said zone mounted for relatively free movement in a direction transversely to the path of travel of the web and in a plane generally parallel to the plane of the web, guide means on said carriage means adapted to extend into and between the folded plies of the web and engage the web at the fold line for causing the carriage to shift laterally on said frame in response to lateral weaving of the fold line of the web as the web travels through said zone, and means carried by and movable with said carriage means for performing said operation on the portion of the web travelling through said zone, said operation performing means being disposed adjacent said guide means so that the operation performing means acts on said web adjacent the portion thereof engaged by the guide means.
 2. The combination called for in claim 1 including means at the inlet and outlet ends of said zone frictionally engaging said web and resisting lateral flexing thereof in response to lateral forces applied to the web by said guide means as the tensioned web travels through said zone.
 3. The combination called for in claim 1 including a roller at the inlet end of said zone around which the web is caused to travel in a tensioned condition, and means for directing the web to said roller such that the web approaches the roller in a plane inclined to the plane of the web as it travels through said zone, said tensioning means causing the web to frictionally engage said roller to minimize the tendency of the web to flex laterally in response to lateral forces applied to the web by said guide means.
 4. The combination called for in claim 1 including a roller adjacent each of the opposite ends of said zone, said rollers extending transversely of the path of travel of the web, said two rollers directing said web in a rectilinear path therebetween so that the web assumes a flat plane at the portion thereof extending beTween the rollers, said web being directed to one of said rollers and away from the other roller at angles inclined to said flat plane so that the tensioning means causes the web to frictionally engage the periphery of said rollers and thus minimize the tendency for the web to flex laterally in response to lateral forces applied thereto by the guide means as the web travels through said zone.
 5. The combination called for in claim 4 wherein said guide means are disposed intermediate said two rollers in the path of travel of the web.
 6. The combination called for in claim 1 wherein said operation performing means comprises a heat sealing member for applying a welded seam to the plastic web in a predetermined position relative to the fold line therein.
 7. The combination called for in claim 1 wherein said web is formed with a V-shaped gusset extending inwardly from a side edge thereof and said guide means extend laterally inwardly of said side edge and engage the fold line defining the apex of the V-shaped gusset.
 8. The combination called for in claim 7 wherein the gusseted portion of the web defines four plies of said web adjacent said one edge and said operation performing means acts upon two of the plies at one side of the guide means.
 9. The combination called for in claim 7 wherein the gusseted portion of the web defines four plies of said web adjacent said side edge, said guide means engaging the fold line of said gusset at two longitudinally spaced portions thereof, said operation performing means being disposed between said longitudinally spaced portions and between the two inner plies of said web.
 10. The combination called for in claim 9 wherein said operation performing means comprises heat sealing means adapted to form a welded seam on the gusseted portion of the web extending inwardly to said fold line in a direction inclined at an acute angle to the path of travel of the web.
 11. The combination called for in claim 1 wherein said web comprises a flattened tubular member having a V-shaped gusset extending laterally inwardly from each side thereof, said guide means comprising a pair of laterally spaced co-planar members extending laterally inwardly from each side edge of the web with the opposite inner edges engaging the opposed vertices of said V-shaped gussets.
 12. The combination called for in claim 11 wherein said carriage means comprises two carriages, one for each guide means, and means for maintaining said guide means in adjustably fixed laterally spaced relation so that the inner opposed edges thereof can be spaced apart in fixed relation to correspond with the lateral spacing between the vertices of webs having differently sized gussets.
 13. The combination called for in claim 12 wherein said last-mentioned means comprises a tie bar interconnecting the two guide means, the interconnection between the tie bar and at least one of said guide means being laterally adjustable.
 14. The combination called for in claim 12 wherein said operation performing means comprises a heat sealing member and a back-up member disposed on opposite sides of said guide means in spaced relation to the opposed outer plies of said web and means for relatively moving the heat sealing member and the back-up member toward each other to form a welded seam on the gusseted portion of the web.
 15. The combination called for in claim 1 wherein the guide means comprises a guide plate extending laterally inwardly between the plies of the web and having an inner guiding edge engaging said fold line, said guiding edge having a recess therein, said operation performing means comprising a heat sealing member, said heat sealing member registering with said recess in the guide plate and extending laterally inwardly to said fold line so that, when the heat sealing member is actuated, it is adapted to form a heat seal extending inwardly from the side edge of the web directly to the fold line.
 16. The combination called for in claim 15 wherein said rEcess is located in said guide edge intermediate the ends thereof.
 17. The combination called for in claim 16 including a sheet of material overlying said recess, said material being of the type to which said plastic web stock will not readily adhere when in a heated condition.
 18. The combination called for in claim 1 wherein the machine includes a second zone having a similar carriage means, guide means and operation performing means at said second zone, said web stock being of flat tubular cross section and having a laterally inwardly extending V-shaped gusset at each side thereof, said guide means at each of said zones engaging the fold lines comprising the vertices of said two gussets, said operation performing means being disposed adjacent one face of the web stock at one of said zones and adjacent the opposite face of the web stock at the other zone.
 19. The combination called for in claim 18 wherein said operation performing means comprises a heat sealing member at each of said zones which when actuated is adapted to form diagonal seals through two plies of the stock at said gussets which extend from the outer side edges of the stock inwardly to the vertices of the gussets.
 20. The combination called for in claim 19 wherein said two zones are spaced apart in the direction of travel of the stock so that the diagonal seals formed between two plies of the stock at one zone register with the diagonal seals formed between the other two plies of the stock at the other zone.
 21. The combination called for in claim 17 wherein said heat sealing member is mounted on said guide plate at said recess and said material overlies opposite faces of the heat sealing member.
 22. The method of aligning a moving web of plastic material having a fold line extending lengthwise thereof in the direction of travel of the web with an apparatus for performing an operation on the web, such as sealing, slitting, printing and the like, comprising the steps of moving the web lengthwise on a support structure in a tensioned condition and in a rectilinear path between two longitudinally spaced points on said support structure, frictionally engaging the web at said two points to minimize the tendency for the web to flex laterally of its direction of travel in response to lateral forces applied to the web between said two points, engaging the fold line of the web with a guide means positioned between said two points, permitting the guide means to shift freely in a lateral direction on said support structure in accordance with lateral movement of the travel of the web between said two points, and supporting said apparatus for free lateral movement with said guide means so that said apparatus is always located laterally in a predetermined position relative to said fold line.
 23. The method according to claim 22 wherein said two points are located on said support structure closely adjacent said guide means on the upstream and downstream sides thereof.
 24. The method according to claim 22 wherein said web is of flat tubular cross section with an inwardly extending V-shaped gusset at each side thereof and said guide means comprises a pair of laterally interconnected guide members extending into said gussets from opposite side edges of the web and engaging the fold lines defined by the apices of the two gussets.
 25. The method according to claim 22 wherein said web comprises a heat sealable plastic film and said apparatus for performing an operation thereon comprises a heat sealing means and including the steps of intermittently arresting the lengthwise movement of said web, relaxing the tension in the web when its lengthwise movement is arrested and causing the heat sealing means to engage the web while the web is in said relaxed condition.
 26. The method according to claim 25 wherein the web is flattened tubular cross section with an inwardly extending V-shaped gusset at each side edge thereof, said guide means comprising a pair of laterally interconnected Guide members extending into said gussets from opposite side edges of the web and engaging the fold lines defined by the apices of the V-shaped gussets and wherein said heat sealing means are caused to engage the gusset portions of the web to form diagonal seals therein extending inwardly from the opposite side edges of the web and terminating at said fold lines. 